Technical Abstract:
Pyrolysis is one of the technologies used in converting biomass to energy. During the process about 15-40% of the initial biomass is recovered as biochar. The pyrolysis process alters feedstock composition and chemistry, rendering its components (e.g. carbon, nutrients) less biodegradable and available. As such, the process is also used to convert organic waste into more stable and recalcitrant biochar product, and hence into a more environmentally sound material to be used in soils. The quality of the biochar as soil amendment and its environmental impact are likely to depend on feedstock source, and the pyrolysis processing conditions. In this study we evaluated the characteristics of biochar derived from chicken litter and alfalfa stems. Chicken litter was processed in slow pyrolysis at 350 and 700 ºC. Chicken litter from additional source and alfalfa stems were processed in fast pyrolysis at 450-500 ºC. Subsamples of all biochars were further steam-activated at 800 ºC. The biochars were analyzed for dissolved carbon content, CaCO3 equivalent (CCE), mineralogical composition, total elemental analysis, and for water, Mehlich-3, Toxicity Characteristics Leaching Procedures (TCLP; EPA Method 1311), and Synthetic Precipitation Leaching Procedures (SPLP; EPA Method 1312) extractable elements. Dissolved carbon content was higher in the fast than in the slow pyrolysis, and it decreased with increasing pyrolysis temperature and with steam activation. Biochar %CCE increased with temperature, and with steam activation (in the case of the 350 ºC chicken litter biochar). Activation increased macro- and micro- nutrients content, while Mehlich-3 extractable concentration decreased (except for K and Mg). The results of the study suggest that pyrolysis processes and biochar management practices need to be further refined in order to assure agronomically beneficial and environmentally safe use of biochar in soil.